Below is a Fischer Esterification reaction. Benzoic acid is refluxed in an exces

Question

Below is a Fischer Esterification reaction. Benzoic acid is refluxed in an excess amount of ethanol with a sulfuric acid catalyst

1. After the quench, the product must be isolated from the reaction mixture. Suppose diethyl ether is added to the quenched reaction mixture. What layer is on the top and what layer is on the bottom (organic or aqueous)? Why?

2. Using your knowledge of acid/base chemistry, what species will be present in the organic layer?

3. What species will be present in the aqueous layer?

4. If leftover starting materials are present, can they be removed via acid/base extraction in the workup? Explain

Explanation / Answer

1. In the reaction, ethanol is taken in excess and no other solvent is used. At the end of the reaction, unreacted ethanol would be left. So, we need to compare the densities of diethyl ether and ethanol to find that which layer would be at the bottom during work up. Density of ethanol is 0.789 g/ml and density of diethyl ether is 0.713 g/ml. So, diethyl ether is lighter than ethanol. Thus, diethyl ether, i.e. organic layer is at the top and ethanol, i.e. aqueous layer is at the bottom. The reason is difference in densities of both solvents.

2. Among the reactants, benzoic acid and the product would be soluble in organic layer. Diethyl ether is non polar and benzoic acid is also nonpolar, so it would be soluble in ether. Product being an organic compound will be soluble in organic layer. So, organic layer would be containing diethyl ether, benzoic acid and product.

3. Aqueous layer would be contaning ethanol and sulfuric acid. These both species are soluble in water.

4. The leftover starting material would be ethanol, as it is taken in excess and sulfuric acid because it is a catalyst. So, at the end of the reaction, ethanol and sulfuric acid would be present which can be removed by neutralizing with some base. And further the reaction products would also be unaffected by addition of a base. Thus, base would be used.

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